Caster locking mechanism and carriage

ABSTRACT

A wheeled carriage has a chassis with a plurality of swivel casters, and a locking assembly actuated by a foot pedal located along the front of the carriage. Pushing down on the foot pedal rotates a cam that engages a cam follower on a &#34;T&#34; bar frame supporting two locking rings which respectively overlie two of the caster wheels to move the rings into a locking position in engagement with the wheels to lock the wheels and the casters in any position. The cam follower surface includes a ramp portion engageable by the cam for driving the rings to their locking position and a horizontal latch portion engageable by the cam in its &#34;overcenter&#34; position for holding the rings in their locking position. A lifter bar is engageable by the user&#39;s foot to rotate the cam back off the follower and permit the rings to resiliently return to their release position. The cam and follower surfaces are so arranged that a limited rotation of the cam through less than about 25 degrees is sufficient to move the assembly between its release and locking configurations so that the locking assembly can be used where only a few inches of clearance beneath the chassis is available.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wheeled carriages of the type whereinthe wheels are in the form of casters. The invention relates inparticular to means for locking the casters so as to prevent rotation ofthe caster wheels and to prevent swiveling motion in the case of swivelcasters.

2. Description of the Prior Art

In caster-wheeled carriages, it is frequently desirable to lock thecaster wheels against rotation for holding the carriage in apredetermined location and preventing any accidental movement thereof.It is well known to provide a separate caster brake or lock for eachcaster wheel. Such brake or lock assemblies are disclosed, for examplein U.S. Pat. No. 3,942,608. It is also known to provide lockingmechanisms which simultaneously lock more than one caster.

This latter type of caster locking mechanism is disclosed, for example,in U.S. Pat. Nos. 3,304,116 and 4,164,355. This type of assemblyprovides a locking ring overlying each of several swivel caster wheelssubstantially coaxially with the caster swivel axis. The locking ringsare all interconnected by a locking frame which is moved by means of acam mechanism between an upper release position wherein the rings areout of contact with the caster wheels to permit free movement thereofand a lowered locking position wherein the rings firmly engage thecaster wheels to prevent rotation thereof and also to prevent swivelingthereof. In that prior art device the locking assembly is actuated by ahandle member which rotates an eccentric cam through an angle of about90° between the release and locking configurations. That arrangement issatisfactory where there is a large amount of under-chassis clearance,such as hospital beds or the like, to accommodate the wide-anglerotation, or where the handle assembly can extend beyond the ends of thechassis.

But that prior arrangement is not suitable for use where there is verylimited clearance which will not permit a full 90° rotation of the cammember. For example, in carriages with low-slung chassis, such as garagemechanic tool chests, there are only a few inches of clearance betweenthe chassis and the floor. This would make it effectively impossible fora user to exert sufficient leverage to rotate a cam mechanism through a90° angle. It would be possible to extend a cam shaft beyond an end ofthe carriage, but this increases the effective floor space occupied bythe carriage and also necessitates that the carriage always be utilizedin an orientation which maintains access to the end from which theactuator shaft projects.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improvedcaster locking assembly which avoids the disadvantages of prior lockingassemblies while affording additional structural and operatingadvantages.

An important feature of the present invention is to provide a casterlocking assembly which can be disposed beneath the chassis of a wheeledcarriage and requires only a few inches of floor clearance for operationthereof.

Still another feature of the invention is to provide a locking assemblyof the type set forth which includes a rotatable cam which requiresrotation through a range of less than 25° to effect operation thereofbetween release and locking configurations.

Still another feature of the invention is the provision of a lockingassembly of the type set forth, which simultaneously locks plural casterwheels against both wheel rotation and caster swiveling.

Another feature of the invention is the provision of a wheeled carriagehaving plural swivel casters which are lockable by a locking assembly ofthe type set forth.

These and other features of the invention are attained by providing, ina caster locking assembly including mounting means adapted to be coupledto an associated load, a caster wheel rotatably carried by the mountingmeans for rolling engagement with an underlying support surface, and alocking ring resiliently carried by the mounting means and overlying thewheel, the locking ring being movable between a release position out ofengagement with the wheel and a locking position firmly frictionallyengaging the wheel for locking thereof, the locking ring beingresiliently biased toward its release position, the improvementcomprising: a cam follower coupled to the locking ring and having afollower surface including an inclined ramp portion, a locking camcarried by the mounting means for rotation about a pivot axis and havinga cam surface disposed for camming engagement with the follower surface,and actuator means coupled to the cam for effecting rotation thereofbetween release and locking conditions, the cam surface being out ofengagement with the follower surface when the cam is disposed in itsrelease condition for permitting the locking ring to move to its releaseposition, movement of the cam from its release condition to its lockingcondition moving the cam surface into camming engagement with the rampportion of the follower surface for driving the locking ring to itslocking position.

The invention consists of certain novel features and a combination ofparts hereinafter fully described, illustrated in the accompanyingdrawings, and particularly pointed out in the appended claims, it beingunderstood that various changes in the details may be made withoutdeparting from the spirit, or sacrificing any of the advantages of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the invention, thereis illustrated in the accompanying drawings a preferred embodimentthereof, from an inspection of which, when considered in connection withthe following description, the invention, its construction andoperation, and many of its advantages should be readily understood andappreciated.

FIG. 1 is a fragmentary, side elevational view of a wheeled carriageincorporating the locking assembly of the present invention, with aportion of the carriage removed;

FIG. 2 is a fragmentary end elevational view of the carriage of FIG. 1,as viewed from the right-hand end thereof;

FIG. 3 is an enlarged, perspective, exploded view of the caster lockingassembly of FIG. 1;

FIG. 4 is an enlarged, fragmentary, bottom plan view of the right-handend of the carriage of FIG. 1;

FIG. 5 is a top plan view of the assembled caster locking assembly ofFIG. 3, removed from the carriage;

FIG. 6 is an enlarged view, similar to FIG. 2, in partial verticalsection, with the locking assembly illustrated in its releaseconfiguration and with the casters swiveled 90° from their positions inFIG. 2;

FIG. 7 is a view similar to FIG. 6, illustrating the locking assembly inits locking configuration;

FIG. 8 is an enlarged, fragmentary view in vertical section takengenerally along the line 8--8 in FIG. 2, and illustrating the lockingassembly in its release configuration; and

FIG. 9 is a further enlarged, fragmentary, perspective view of thecooperation of the cam and cam follower of the present invention in thelocking configuration of the locking assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1, 2, 4 and 6-8, there is illustrated a wheeledcarriage, generally designated by the numeral 10, which includes anelongated, substantially rectangular chassis 11 provided with a bottomwall 12 having a raised central portion 14 (FIGS. 4 and 8). The chassis11 includes a pair of longitudinally extending angles 15 along eitherside of the raised central portion 14, the angles 15 being connectedintermediate the ends thereof by a transverse channel member 16 whichhas a pair of parallel vertical side walls 17 interconnected by a bottomwall 18.

Mounted on the chassis 11, respectively adjacent to the four cornersthereof, are four casters, including two swivel casters 20 at one end ofthe chassis 11 and two fixed casters 20A at the other end of the chassis11 (FIG. 1). Each of the casters 20 and 20A includes a yoke 21 having abight portion 22 (FIG. 6) which, in the case of the swivel casters 20,is fixedly secured to a swivel plate 23 mounted on the bottom wall 12 ofthe chassis 11 for rotation about a swivel axis 28 (FIG. 6). In the caseof the fixed casters 20A, the bight 22 is fixedly secured to the bottomwall 12 of the chassis 11. The yoke 21 also includes a pair of legs 24depending, respectively, from the opposite ends of the bight 22, thelegs 24 being substantially vertical in the case of the fixed casters20A and being inclined to the vertical in the case of the swivel casters20. Disposed between the legs 24 is a wheel 25 rotatable about ahorizontal axle 26, the opposite ends of which are journaled in the legs24. If desired, any one or more of the casters 20 and 20A may beprovided with an individual wheel lock 27 (see FIGS. 6-8), but this isoptional. In use, it will be appreciated that the wheels 25 are adaptedfor rolling engagement with an underlying support surface, such as afloor 29 (FIGS. 6-8), for moving the carriage 10, it being appreciatedthat steering of the carriage 10 is permitted by the swivel action ofthe casters 20.

Referring now also to FIGS. 3, 5 and 9, the carriage 10 includes acaster locking assembly, generally designated by the numeral 30,constructed in accordance with and embodying the features of the presentinvention. The locking assembly 30 includes a frame 31 in the form of a"T" bar (FIGS. 4 and 5), which includes an elongated bar 32 extendinglongitudinally of the chassis 11 and provided at one end thereof with anupstanding mounting flange 33 which is fixedly secured to one of theside walls 17 of the channel 16 by suitable fasteners 34 (FIG. 8).Integral with the bar 32 at the other end thereof is an upstanding guideflange 33a, having a guide slot 34a in the upper edge thereof, centrallythereof. The frame 31 also includes a cross bar 35 which extends betweenthe swivel casters 20 substantially normal to the bar 32, and includes aflat central portion 36 integral at its opposite ends, respectively,with a pair of upwardly inclined shoulders 37, which are in turnintegral with raised horizontal end portions 38. The central portion 36is fixedly secured to the distal end of the bar 32 by suitable fasteners39 (FIG. 4). One or more shims 40 may be disposed between the cross bar35 and the bar 32 for proper adjustment thereof in a manner to bedescribed more fully below, each of the shims 40 having an elongatedlongitudinal slot 41 therein to receive the fasteners 39 therethrough.The slots 41 permit the shims 40 to be added or removed by simplyloosening the fasteners 39 without disassembly of the frame 31. The endportions 38 of the cross bar 35 are respectively integral with twolocking rings 43 and 44, which are respectively disposed above thewheels 25 of the swivel casters 20 in encircling relationship with theyokes 21 and respectively substantially coaxial with the swivel axes 28.

A cam follower 45 is mounted on the upper surface of the bar 32 adjacentto the distal end thereof by means of the fasteners 39. The cam follower45 is an elongated, generally oval body having an inclined ramp surface46 formed in one side thereof, the upper end of the ramp surface 46intersecting a horizontal latch surface 47 which is recessed below theupper surface of the cam follower 45, being spaced therefrom by avertical stop surface 48 (see FIGS. 3 and 9).

The locking assembly 30 also includes an elongated cam shaft 50 whichextends through a complementary bore 51 in the mounting flange 33 of thebar 32 and projects forwardly above the bar 32 through a complementaryguide slot 52 in the bottom edge of a mounting block 53, which isfixedly secured to the bottom wall 12 of the chassis 11 by suitablefasteners 54 (FIG. 4), and thence through the guide slot 34a in theguide flange 33a of the bar 32. The shaft 50 is freely rotatable aboutits axis in the bore 51 and the slots 34a and 52 and has a cam 55fixedly secured thereto between the guide flange 33a and the mountingblock 53. The cam 55 has a part-cylindrical body 56 which is coaxialwith the shaft 50, and has projecting therefrom a triangular tip 57which has a pair of flat side surfaces 58 which converge to a tipsurface 59 (FIGS. 3 and 9). The cam 55 is positioned immediately abovethe cam follower 45 for engagement of one of the side surfaces 58 andthe tip surface 59 of the cam 55 with the ramp surface 46 and the latchsurface 47 of the cam follower 45, as will be described in greaterdetail below.

Rotation of the shaft 50 and the cam 55 is effected by means of a crankarm 60 which is unitary with the end of the shaft 50 projecting beyondthe attachment flange 33 of bar 32. The crank arm 60 extendssubstantially perpendicular to the longitudinal axis of the shaft 50 tothe front side of the carriage 10, and is provided at its distal endwith a pedal portion 61 which is disposed substantially normal to thecrank arm 60. The crank arm 60 is also provided with a lifter bar 62which has an attachment portion 63 fixedly secured to the crank arm 60,as by welding, adjacent to the pedal portion 61, but extending in theopposite direction therefrom. The lifter bar 62 is elevated apredetermined distance over the pedal portion 61.

Preferably, the bar 32 is preloaded, i.e., it is bent so that it isinclined at an angle of slightly less than 90° with the attachmentflange 33 and at an angle of slightly greater than 90° with the guideflange 33a. Thus, in its mounted condition, with the flanges 33 and 33Adisposed vertically, the bar 32 is normally disposed in a releaseposition (FIGS. 1, 6 and 8) inclined slightly upwardly. Preferably, thebar 32 is formed of a resilient material, such as steel, so as toaccommodate deflection downwardly from its normal release position, andto act essentially as a leaf spring inherently biased back to its normalrelease position. In this normal release position, the locking assembly30 is disposed in a release configuration, wherein the locking rings 43and 44 are respectively spaced a slight distance above the caster wheels25, out of engagement therewith, for accommodating free rotation thereofand free swiveling movement thereof (FIGS. 6 and 8). Adjustment of thisrelease position to obtain the proper clearance between the lockingrings 43 and 44 and the wheels 25 can be effected by insertion orremoval of shims 40.

The carriage 10 may be any type of carriage, but in the preferredembodiment it is in the form of a mechanics' tool chest of the typeutilized by automotive mechanics in automotive garages and the like. Insuch carriages, there is typically only a four or five-inch clearancebetween the chassis 11 and the floor 29. In use, the crank arm 60 is sopositioned that the pedal portion 61 is disposed adjacent to the frontwall of the carriage 10 so that, when the crank arm 60 is in its normalrelease condition (FIGS. 1 and 2) the pedal portion 61 is spacedslightly below the chassis 11 a distance sufficient for a user to inserthis foot to depress the pedal portion 61, thereby rotating the shaft 50about its axis in a counterclockwise direction, as viewed in FIGS. 6-8.The cam 55 is fixed so that when the crank arm 60 is disposed in itsnormal release condition, the cam 55 is in the position illustrated inFIGS. 6 and 8, with its inner side surface 58 disposed closely adjacentto, but not necessarily in contact with the inclined ramp surface 46 ofthe cam follower 45.

When the crank arm 60 is depressed by the user's foot, the side surface58 of the cam 55 moves into camming engagement with the inclined rampsurface 46 of the cam follower 45, depressing the cam follower 45 and,thereby, the locking frame 31. As the rotation of the cam 55 continues,the tip surface 59 thereof moves into engagement with the ramp surface46 and cams upwardly along it and then rides up onto the horizontallatch surface 47. At this point, the cam 55 is in an "over-center38condition, wherein a line extending through the axis of the shaft 50 andthe line of contact between the tip surface 59 and the latch surface 47will be substantially vertical.

In this condition, the locking assembly 30 is in a locking configuration(FIG. 7), wherein the pedal portion 61 is closely adjacent to the floor29, and wherein the locking rings 43 and 44 have been respectively moveddown into firm frictional engagement with the wheels 25 of the swivelcasters 20. Further rotation of the cam 55 beyond this lockingconfiguration is prevented by engagement of the side surface 58 of thecam 55 with the stop surface 48 of the cam follower 45 (FIG. 9). It willbe appreciated that during depression of the crank arm 60 by the usersfoot, vertical and lateral movements of the shaft 50 are effectivelyprevented by the mounting block 53 and the guide flange 33A. It willfurther be noted that the locking assembly 30 is effective for lockingthe swivel casters 20 in any swivel position thereof and effectivelypreventing not only rotation of the wheels 25 about the axles 26, butalso preventing swiveling of the casters 20.

Because of the cooperation of the cam 55 and the cam follower 45, it isonly necessary to rotate the shaft 50 through a limited angle ofsubstantially less than 45° to effect movement of the locking assembly30 from its release configuration to its locking configuration. In thepreferred embodiment of the invention, it has been found that rotationalmovement through an angle of about 22° is sufficient. However, even withthis limited rotational movement, substantially all of the availableclearance between the chassis 11 will be used, so that in the lockingconfiguration of the locking assembly 30, the pedal portion 61 will bedisposed very closley adjacent to the floor 29. However, the elevatedposition of the lifter bar 62 relative to the pedal portion 61 providessufficient clearance from the floor 29 to permit the user to insert hisfoot beneath the lifter bar 62 to pivot the crank arm 60 back up to itsnormal release condition to move the locking assembly 30 back to itsrelease configuration to unlock the casters 20.

In a constructional model of the present invention, the cam follower 45and the mounting block 53 are formed of suitable low-friction plasticmaterial, such as nylon. The bar 32 and the cam 55 may be formed ofsteel. The clearance beneath the chassis 11 is 4 or 5 inches and thelocking rings 43 and 44 move about one-quarter inch between theirrelease and locking positions. The height of the cam follower 45 isabout 0.2 inch and the cam 55 measures about 1.15 inch from its pivotaxis to the tip surface 59.

From the foregoing, it can be seen that there has been provided animproved caster locking assembly which provides efficient foot-pedaloperation between release and locking configurations for simultaneouslylocking plural swivel casters by rotation of a cam through a limitedangle, so as to be operable where only limited floor clearance isavailable.

.[.We claim.]. .Iadd.What is claimed is.Iaddend. :
 1. In a casterlocking assembly including mounting means adapted to be coupled to anassociated load, a caster wheel rotatably carried by the mounting meansfor rolling engagement with an underlying support surface, .Iadd.thecaster having a swivel yoke supporting the caster wheel and carried bythe mounting means for rotation about a swivel axis, .Iaddend.and alocking ring resiliently carried by the mounting means.Iadd.substantially coaxially with the swivel axis .Iaddend.andoverlying the wheel, the locking ring lying in a plane and .Iadd.havinga central axis substantially perpendicular to said plane and.Iaddend.being movable between a release position out of engagement withthe wheel and a locking position firmly frictionally engaging the wheelfor locking thereof, the locking ring being resiliently biased towardits release position, the improvement comprising: a cam follower coupledto the locking ring and having a follower surface including .[.aninclined.]. .Iadd.a planar .Iaddend.ramp portion .Iadd.inclined withrespect to said plane,.Iaddend.a locking cam carried by the mountingmeans for rotation about a pivot axis inclined with respect to thedirection of movement of the locking ring and having a cam surfacedisposed for camming engagement with said follower surface, and actuatormeans coupled to said cam for effecting rotation thereof between releaseand locking conditions, .[.said cam surface being out of engagement withsaid follower surface when said cam is disposed in its release conditionfor permitting the locking ring to move to its release position,.].movement of said cam from its release condition to its locking conditionmoving said cam surface .[.into.]. .Iadd.in .Iaddend.camming engagementwith said ramp portion of said follower surface for driving the lockingring to its locking positioni , whereby the locking ring in its lockingposition effectively prevents swiveling of the caster. .[.
 2. The casterlocking assembly of claim 1, wherein the caster includes a swivel yokesupporting the caster wheel and carried by the mounting means forrotation about a swivel axis, the locking ring being disposedsubstantially coaxially with the swivel axis and, in its lockingposition, effectively preventing swiveling of the caster..].
 3. Thecaster locking assembly of claim 1, wherein said cam follower includes alatch portion intersecting said ramp portion at the upper end thereofand engageable by said cam surface for holding the locking ring in itslocking position.
 4. The caster locking assembly of claim 3, whereinsaid follower surface further includes a stop portion intersecting saidlatch portion and engageable with said cam surface for limiting therotational movement of said cam.
 5. The caster locking assembly of claim1, wherein said cam has a part-circularly cylindrical portion coaxialwith said pivot axis and a generally triangular prismatic tip portionprojecting from said body portion for engagement with said cam follower.6. The caster locking assembly of claim 3, wherein said actuator meansincludes a locking shaft carried by the mounting means for rotationabout the pivot axis, said cam being carried by said shaft for rotationtherewith.
 7. The caster locking assembly of claim 6, wherein saidactuator means further includes foot pedal means projecting from saidlocking shaft substantially normal to the pivot axis for access by thefoot of a user, said foot pedal means being depressible by the user'sfoot to rotate said locking cam from its release condition to itslocking condition.
 8. The caster locking assembly of claim 7, whereinsaid actuator means further includes a lifter bar projecting laterallyfrom said foot pedal means and elevated a predetermined distancethereabove sufficient so that when said locking cam is disposed in itslocking condition there is sufficient clearance beneath said lifter barfor insertion of a user's foot for lifting of said actuator means torotate said locking cam from its locking condition back to its releasecondition.
 9. In a caster locking assembly including mounting meansadapted to be coupled to an associated load, a pair of caster wheelsrespectively rotatably carried by the mounting means for rollingengagement with an underlying support surface, a locking frameresiliently supported by the mounting means, and a pair of locking ringscarried by the locking frame .Iadd.and lying in a plane .Iaddend.andrespectively overlying the wheels .Iadd.and having substantiallyparallel central axes substantially perpendicular to saidplane.Iaddend., the locking frame being movable between a releaseposition wherein the locking rings are out of engagement with the wheelsand a locking position wherein the locking rings respectively firmlyfrictionally engage the wheels for locking thereof, the locking framebeing resiliently biased toward its release position, the improvementcomprising: a cam follower carried by the locking frame and having afollower surface including .[.an inclined.]. .Iadd.a planar.Iaddend.ramp portion .Iadd.inclined with respect to saidplane.Iaddend., a locking cam carried by the mounting means for rotationabout a pivot axis inclined with respect to the direction of movement ofthe locking rings and having a cam surface disposed for cammingengagement with said follower surface, and actuator means coupled tosaid cam for effecting rotation thereof between release and lockingconditions, .[.said cam surface being out of engagement with saidfollower surface when said cam is disposed in its release condition forpermitting the locking frame to move to its release position,.].movement of said cam from its release condition to its locking conditionmoving said cam surface .[.into.]. .Iadd.in .Iaddend.camming engagementwith said ramp portion of said follower surface for driving the lockingframe to its locking position.
 10. The caster locking assembly of claim9, wherein the caster includes a swivel yoke supporting the caster wheeland carried by the mounting means for rotation about a swivel axis, thelocking ring being disposed substantially coaxially with the swivel axisand, in its locking position, effectively preventing swiveling of thecaster.
 11. The caster locking assembly of claim 9, wherein said pivotaxis substantially bisects a line which interconnects the swivel axesand is substantially perpendicular thereto.
 12. The caster lockingassembly of claim 9, wherein said follower surface includes a latchportion intersecting said ramp portion at the upper end thereof andengageable by said cam surface for holding the locking frame in itslocking position.
 13. The caster locking assembly of claim 9, whereinthe locking frame is in the form of an elongated resilient metal bar.[.couple.]. .Iadd.coupled .Iaddend.at one end thereof to the mountingmeans in cantilever fashion and carrying the locking rings and said camfollower adjacent to the other end thereof, said bar being normallydisposed in the release position of the locking frame and beingresiliently deflectable from that position.
 14. In a wheeled carriageincluding a chassis, a plurality of swivel yokes carried by the chassisfor rotation respectively about substantially parallel swivel axes, aplurality of wheels respectively carried by the yokes for rotation aboutaxes disposed substantially perpendicular respectively to the swivelaxes, a locking frame resiliently supported by the chassis, and at leasttwo locking rings carried by the locking frame and respectivelyoverlying at least two of the wheels substantially coaxially with thecorresponding swivel axes, the locking frame being movable between arelease position wherein the locking rings are out of engagement withthe associated wheels and a locking position wherein the locking ringsfirmly frictionally engage the associated wheels for locking thereof,the locking frame being resiliently biased toward its release position,the improvement comprising: a cam follower carried by the locking frameand having a follower surface including .[.an inclined.]. .Iadd.a planar.Iaddend.ramp portion .Iadd.inclined with respect to a plane which issubstantially perpendicular to the swivel axes.Iaddend., a locking camcarried by the chassis for rotation about a pivot axis inclined withrespect to the direction of movement of the locking rings and having acam surface disposed for camming engagement with said follower surface,and actuator means coupled to said cam for effecting rotation thereofbetween release and locking conditions, .[.said cam surface being out ofengagement with said follower surface when said cam is disposed in itsrelease condition for permitting the locking frame to move to itsrelease position,.]. movement of said cam from its release condition toits locking condition moving said cam surface .[.into.]. .Iadd.in.Iaddend.camming engagement with said ramp portion of said followersurface for driving the locking frame to its locking position.
 15. Thecarriage of claim 14, wherein the chassis .[.i.]. .Iadd.is.Iaddend.generally rectangular in shape, the at least two wheels beingdisposed at one end of the chassis.
 16. The carriage of claim 14,wherein said actuator means includes a locking shaft carried by thechassis for rotation about said pivot axis, said cam being carried bysaid shaft for rotation therewith, foot pedal means projecting from saidlocking shaft substantially perpendicular to said pivot axis toward thefront of the chassis for engagement and depression by the foot of a userto rotate said cam from its release condition to its locking condition.17. The carriage of claim 16, wherein said actuator means furtherincludes a lifter bar projecting laterally from said foot pedal meansand elevated a predetermined distance thereabove sufficient to permitinsertion of a user's foot beneath said lifter bar when said cam isdisposed in its locking condition for lifting of said actuator means torotate said cam from its locking condition to its release condition. 18.The carriage of claim 16, wherein the locking frame includes meansrotatably supporting said shaft adjacent to one end thereof, and furthercomprising auxiliary support means carried by the chassis for rotatablysupporting said shaft adjacent to the other end thereof.
 19. Thecarriage of claim 18, and further comprising guide means carried by thelocking frame and cooperating with said shaft to inhibit lateralmovement of the locking frame during operation of said actuator means.20. The carriage of claim 14, wherein the locking frame is in the formof an elongated resilient metal bar coupled at one end thereof to thechassis in cantilever fashion and carrying the locking rings and saidcam follower adjacent to the other end thereof, said bar being normallydisposed in the release position of the locking frame and beingresiliently deflectable from that position.
 21. The carriage of claim14, wherein said cam rotates through an angle of less than 25 degreesbetween the release and locking conditions thereof.